In the prior art, a variety of hydrogensiloxanes were proposed as well as their preparation processes. Japanese Patent Application Kokai Nos. 47605/1987, 47608/1987 and 49305/1987 disclose hydrogensiloxanes of formula (3), which are synthesized by hydrolyzing a solution of a chlorosilane of formula (4) and dimethylchlorosilane of formula (5) in trifluorotrichloroethane. ##STR3## In the formulae, R'f is C.sub.6 F.sub.12 which is a perfluoroalkylene group, and n is equal to 1, 2 or 3.
Dimethylchlorosilane of formula (5) forms in a minor amount during preparation of silicones by the direct process, but is very difficult to separate and isolate from low boiling fractions of hydrocarbon. Another known process for the synthesis of dimethylchlorosilane of formula (5) is by reacting dichlorosilane with 1,1,3,3-tetramethyldisiloxane in the presence of a catalyst. In either case, dimethylchlorosilane is available at an increased cost and less advantageous as a source material. The possibility that the dimethylchlorosilane of formula (5) condense into polysiloxane by-products is also a problem.
The above-referred patent publications disclose specific examples of synthesizing hydrogensiloxanes of formula (3) wherein R'f is a perfluoroalkylene group, but not hydrogensiloxanes wherein R'f is a perfluoropolyether group. In this regard, hydrogensiloxanes of formula (3) wherein R'f is a perfluoropolyether group are not disclosed in a substantial sense.